Improvement in tunability and dielectric loss of BSTZ ferroelectric thin films using post-annealing

Abstract

The change in dielectric constant of ferroelectric materials as a function of electric field is the key to wide range of applications such as tunable oscillators, delay lines, and phase shifters. The effect of the post-annealing on the dielectric properties of (Ba0.6Sr0.4)(Ti0.9Zr0.1)O-3 (BSTZ) thin films deposited by Pulsed Laser Deposition is studied. BSTZ ferroelectric thin films showed simple cubic perovskite structure having (200) preferred orientation independent on deposition conditions. Preferred orientation slightly increased after post-annealing. With increasing the oxygen pressure, the dielectric loss of ferroelectric thin films decreased due to the oxygen vacancies. The reason why the dielectric constant increased was due to expansion of unit cell volume leading the increase of ion polarizability. The structure of ferroelectric thin film did not change after post-annealing. The grain size, dielectric constant and tunability were increased; however dielectric loss was decreased after annealing. The microstructure of ferroelectric thin film was one of the important facts(stress between thin films and substrates, thermal conductivity etc) effecting the dielectric properties such as dielectric constant, dielectric loss and tunability etc. Microwave dielectric properties of (Ba0.6Sr0.4)(Ti0.9Zr0.1) O-3 ferroelectric thin film were obtained at deposition temperature 750 degrees C, oxygen pressure 200 mTorr, and post-annealing conditions 1100 degrees C for 1h : dielectric constant 2060, dielectric loss 0.0026 and tunability 25.3%.